Formation of Al–Al₂O₃ core–shell nanosphere chains during electron beam melting of γ-TiAl

Several core–shell nanosphere chains were observed in the electron beam melted Ti–48Al–2Cr–2Nb samples. The formation mechanism of such core–shell nanospheres, induced by Al vaporization, during the electron beam melting of γ-TiAl was investigated using the HRTEM, FESEM, STEM, and XRD analyses. The solidification of TiAl/Ti₃Al lamellae, in the vicinity of the Al-diminished zones, was disclosed by microstructural studies. The core and shell of the nanospheres were characterized as porous Al and α-Al₂O₃, respectively. Finally, the formation of core–shell nanosphere chains in the additive manufactured γ-TiAl was schematically illustrated.